The continuous controlled delivery of drugs through the derma, i.e., skin, provides many advantages over other routes of administration. Transdermal drug delivery is a comfortable, convenient, and noninvasive alternative to other means of drug delivery such as by ingesting medication at fixed time intervals orally or by way of subcutaneous injection. Transdermal drug delivery systems not only allow the controlled release of a pharmaceutical product in a sustained release fashion, but reduce side effects such as gastrointestinal irritation, avoid hepatic first-pass inactivation, poor or erratic absorption from the gastrointestinal tract, and inactivation by the gastrointestinal fluids. Transdermal drug delivery also makes possible a high degree of control over blood concentrations of any particular drug. These advantages enhance patient compliance and improve the safety and efficacy of medications.
In transdermal drug delivery systems, drugs are delivered from a patch applied to the skin with a pressure sensitive adhesive. Useful adhesives are permanently tacky at room temperature, hold the transdermal system to the skin with gentle pressure, and can be easily removed without causing pain or depositing adhesive residue. Devices for transdermal delivery of drugs generally fall into either the category of liquid reservoir patches or matrix patches. The simplest form of matrix patch uses the adhesive itself as the carrier for a drug. In a liquid reservoir patch, the drug is dissolved or dispersed in a liquid reservoir compartment, either totally covered by a rate controlling membrane, or in a polymer matrix. While reservoir systems may use only a peripheral adhesive ring for attachment to the skin surface, a face adhesive which coats both the drug releasing surface and the area surrounding it is often used. Thus, in both matrix- and reservoir-type patches ingredients formulated into the transdermal delivery device, i.e., drugs and various excipients including cosolvents and skin penetration enhancers, must diffuse through the skin contact adhesive in reservoir-type systems and diffuse from the adhesive in matrix-type systems.
Some adhesives may, however, chemically react with various drugs, skin penetration enhancers and excipients in the transdermal system. For example, basic amine functional drugs can react with the acidic moieties of an acrylic adhesive causing a lack of adhesion and tack even before the device is applied to the patient's skin. Moreover, the reactivity of active ingredients within a transdermal drug delivery system with the polymer backbone or side group and with residual monomer could cause degradation and/or binding of the drug and, therefore, is a threat to sustained release and limits the application of this technology. A second area of concern to transdermal patch formulators is the formation of new compounds within the patch as a result of a chemical reaction between the active ingredients and the adhesive. These new compounds may be physiologically active in the body and cause deleterious effects.
The known advantages of continuous transdermal drug delivery devices has prompted the development of transdermal drug delivery systems for the administration of a variety of drugs. While acrylic adhesives for transdermal applications are known, and a number of transdermal drug delivery systems are currently available commercially, there remains a need in the art for a non-reactive adhesive composition for use in transdermal drug delivery systems so that this technology can be extended and used as a delivery option for an even broader range of drugs.